St. Louis, March 30, 2009 —A new theory about sleep's benefits for the brain gets a boost from fruit flies in this week's Science. Researchers at Washington University School of Medicine in St. Louis found evidence that sleep, already recognized as a promoter of long-term memories, also helps clear room in the brain for new learning.

The critical question: How many synapses, or junctures where nerve cells communicate with each other, are modified by sleep? Neurologists believe creation of new synapses is one key way the brain encodes memories and learning, but this cannot continue unabated and may be where sleep comes in.

"There are a number of reasons why the brain can't indefinitely add synapses, including the finite spatial constraints of the skull," says senior author Paul Shaw, Ph.D., assistant professor of neurobiology at Washington University School of Medicine in St. Louis. "We were able to track the creation of new synapses in fruit flies during learning experiences, and to show that sleep pushed that number back down."

This isn't the first research result I've come across that supports this idea. You sleep and lots of less important memories of the day basically get tossed out. You wake up the next day with a less cluttered mind better prepared to record a new set of events.

Infants spend more time in REM sleep than adults, and a lack of REM sleep is associated with depression. Dreaming is a problem solver, to help in our survival, so sleep disorders could be detrimental to our mental health and our ability to learn.